GNU Info

(libc.info)Variadic Prototypes

---

Next: Receiving Arguments Up: How Variadic

---

Enter node , (file) or (file)node

Syntax for Variable Arguments
.............................

   A function that accepts a variable number of arguments must be
declared with a prototype that says so.   You write the fixed arguments
as usual, and then tack on `...' to indicate the possibility of
additional arguments.  The syntax of ISO C requires at least one fixed
argument before the `...'.  For example,

     int
     func (const char *a, int b, ...)
     {
       ...
     }

defines a function `func' which returns an `int' and takes two required
arguments, a `const char *' and an `int'.  These are followed by any
number of anonymous arguments.

   *Portability note:* For some C compilers, the last required argument
must not be declared `register' in the function definition.
Furthermore, this argument's type must be "self-promoting": that is,
the default promotions must not change its type.  This rules out array
and function types, as well as `float', `char' (whether signed or not)
and `short int' (whether signed or not).  This is actually an ISO C
requirement.